RECOVERING Vista Product Key

I had some issues with my drive, (or so my semi-computer literate friend says) and had to reinstall Vista. Now it's asking me for my product key and - forget it - there's NO WAY I can remember what happened to it. I have seen that there are some apps that allow you to recover? your key from your system (mine was valid) however I dunno if there's one in particular someone more educated on the matter could direct me to.
I have had to relinquish command from my friend who after 4 days hasn't been able to get my computer past it's "limited functionality" mode and it's really pissing me off. I have 7 days left to rewrite my grant proposal and I NEED my computer to be working yesterday. So if someone could help me out because I signed up for your community and everything and I'd hate to have wasted more time than I already have. Please spare me the techie diatribe, I'm not completely retarded but I will get lost if it gets too technical. Thank you kindly, R.
Also: Vista Home Premium Edition.